The present invention relates generally to alternators for use in motor vehicles and, more particularly, to a method and apparatus for operating an alternator in a motor vehicle to improve low engine speed power generation and to do so in a compact alternator structure.
A conventional motor vehicle alternator is driven by the vehicle's internal combustion engine at a defined speed change ratio through a drive belt or the like. Unfortunately, the output current and efficiency of the alternator vary with the speed of the engine which is controlled for the mechanical requirements of the vehicle. At low speeds, the alternator output is insufficient to provide the power needed to operate all electrical equipment of the vehicle while at high speeds, power generation is sufficient to far exceed these requirements.
It has been recognized that the operating speed of an alternator used in the electrical system of a motor vehicle may be varied to overcome these inconsistent power generation versus power requirements and to advantageously generate sufficient power for the motor vehicle when the engine is operating at a low speed. For example, a two speed alternator operable at its higher speed for low speed operation of the corresponding motor vehicle engine is known. In the known system, switches between the low and high speeds are performed by a centrifugal switch at a given engine speed.
Another two speed alternator system provides switches between a high speed and a low speed dependent upon detection of idling operation of the driving engine.
Still another alternator speed control arrangement involves an alternator speed changing device which is controlled to maintain operation of an alternator within an optimum predetermined range of operating speeds at all times.
While not related to the problem of providing sufficient power at low operating speed of a driving internal combustion engine, an alternator control system is known which prevents over-speed operation of an alternator. In this system, the frequency of the output power from the alternator is monitored and an alternator drive system is disengaged for frequencies above a given frequency. Hence, operation of the alternator above a given speed is prevented to thereby prevent potential damage to the alternator.
These known alternator control arrangements are useful in providing adequate power at low engine speeds or for protecting alternators at high engine speeds; however, the known alternator control arrangements for providing adequate power at low engine speeds are either mechanically unreliable or require control inputs from an engine speed controller or the like for proper operation.
Accordingly, there is a need for an improved control arrangement for controlling the operation of an alternator in a motor vehicle which is reliable and does not require interconnection to related engine operating components. Preferably, the improved arrangement would permit a compact alternator structure to not only provide adequate power at low engine operating speeds but also occupy less space within the engine compartment.